Fact: Americans love to look at photos of presidents at the beginning and end of their Oval Office terms and point out how much their stress of the job seems to have aged them. But science has yet to prove that daily stresses cause hair to turn gray prematurely. The age at which your locks turn gray, research shows, depends more on genetics than lifestyle.

Hair turns gray when the cells responsible for hair color stop producing pigment, and the average age when this happens varies by ethnicity. Research published in 2005 in the Journal of Investigative Dermatology, said white people, on average, tend to gray first, in their mid-30s, followed by Asians in their late 30s and blacks in their mid-40s. By age 50, half of all people have half-gray heads. Most U.S. presidents serve during the years when gray strands naturally outnumber colored ones. Source: bit.ly/VbDsZu.

For further evidence of the role genes play in gray, scientists in a 2009 Danish study examined more than 100 pairs of identical and fraternal twin sisters. Identical twins, who share the same genes, grayed at very similar rates regardless of lifestyle differences, while fraternal twins, whose genes differ, turned gray at different rates. Source: bit.ly/4zRjL4.

Some recent research has indicated that gray hair might appear faster if a person's cells are "stressed." Cellular stress can result from a variety of causes, from vitamin deficiencies to exposure to the sun's radiation to smoking. Source: bit.ly/TyhCAf.

And there's some good news for people genetically predisposed to turn gray young: It's not a sign that the rest of your body is aging faster than normal. One 1991 study examined the autopsies of 200 patients who died after age 40 and determined that people with prematurely gray hair did not die at younger ages. Source: 1.usa.gov/TyhMrh.

In 1996, researchers in Copenhagen followed 20,000 men and women and determined that outward signs of aging, including gray hair, baldness or facial wrinkles, did not increase a person's likelihood of early death from a heart condition. Source: 1.usa.gov/UwX3VF.